You are experiencing the same condition that I encountered with the 8411's and the Futaba Rx several years ago. Occasional to severe glitching, with a reply to a similar question sent to JR like you received. The same question sent to Futaba received the reply "that sometimes long servo leads cause radio interference" Never could figure out how she equated the servo leads with the problem I had at the time.

The solution was simple, either change out the servos to another brand or change radio systems used.

Pat